System and method for passive normalization of a probe

ABSTRACT

A system and method passively normalize an ultrasonic dry coupled wheel probe as the probe traverses a surface of a structure to inspect the structure, such as a flat structure or a curved pipe. At least a pair of arms are configured to passively maintain normalization of the probe in a detection direction normal to the surface.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wheel probes for inspectinga structure, and, more particularly, to a system and method for passivenormalization of an ultrasonic dry coupled wheel probe as the probeinspects a structure.

BACKGROUND OF THE DISCLOSURE

In various technical fields, such as the oil and gas industry, pipelinesand other structures are inspected using sensors. In ultrasonic testing(UT), such sensors utilize ultrasonic waves to penetrate the surface ofstructures. UT-based sensors are known for providing a non-destructivetesting technique for such inspections of structures. For example, wheninspecting a steel structure such as a steel pipe, a UT-based sensortraverses the surface of the structure to measure the thickness of thesteel to determine whether the thickness has reduced below a certaincritical limit due to erosion. By periodically performing suchnon-destructive and surface penetrating inspections, the steel structurecan be evaluated to avoid leaks, failures, and unplanned shutdowns ofthe pipe during operation.

UT-based sensors can be directional sensors, such as ultrasonic drycoupled wheel probes. Such wheel probes are capable of traversing anytype of surface, such as a flat surface or a curved surface of a pipe.The wheel probes can be incorporated into a crawler-type device whichmoves upon the surface of the structure being inspected. However, suchdirectional sensors require normalization of the sensors in order toensure that the generated ultrasonic waves from the probe are directednormal, that is, perpendicular to the surface under test. Such normalemissions permit the reflection of the ultrasonic waves from thestructure to be redirected back to the sensor. A slight inclination ofthe direction of the emission of the ultrasonic waves can cause the lossof the reflected signal. Accordingly, recalibration of known probes withsensors is often required as the probes traverse surfaces havingdifferent curvatures.

One technique to recalibrate a probe is to use an actuator for activelynormalizing the probe towards a given surface. However, such actuatorsincrease the size and cost of the probe or the crawler in which theprobe is mounted. In addition, such actuators must be activated everytime for different curvatures of the surface under test. It is inrespect of these problems in the art that the present disclosure isdirected.

SUMMARY OF THE DISCLOSURE

According to an embodiment consistent with the present disclosure, asystem and method passively normalize an ultrasonic dry coupled wheelprobe as the probe traverses a surface of a structure to inspect thestructure, such as a flat structure or a curved pipe. At least a pair ofarms are configured to passively maintain normalization of the probe ina detection direction normal to the surface.

In an embodiment, an assembly configured to hold a probe adjacent to atest surface. The assembly comprises a first connector, first and secondarms, a pair of first mounting members, a pair of first wheels, and aholder. The first arm is pivotably coupled to the first connector at afirst end thereof. The first arm extends in a forward direction andextends in a normal direction perpendicular to the forward direction andnormal to the test surface. Similarly, the second arm is pivotablycoupled to the first connector at a first end thereof. The second armextends in a rearward direction opposite to the forward direction andextending in the normal direction.

In a more particular embodiment, each of the pair of first mountingmembers is coupled to a respective second end of the first and secondarms, each of the pair of first wheels is coupled to a respective firstmounting member, the holder is coupled to the first connector and isconfigured to hold the probe, the pivotable coupling of the first andsecond arms to the first connector passively normalizes a detectiondirection of the probe as the probe traverses the test surface, or acombination of these further arrangements can be used in a givenembodiment.

In additional, particular embodiments, the first connector can include afirst pinion gear, the pair of first wheels can be casters, the holdercan be coupled to a rotating shaft of the probe and can be configured toallow the probe to rotate around the rotating shaft, a first resilientmember can connect to each of the first and second arms and the firstresilient member can be configured to bias the first and second armstowards each other, the first and second arms can pivot with a firstdegree of freedom in the forward and rearward directions, respectively,or a combination of these further arrangements can be used in a givenembodiment, including with any of the embodiments described above

In an alternative embodiment, the assembly includes a second connector,third and fourth arms, a pair of second mounting members, and a pair ofsecond wheels. The third arm is pivotably coupled to the secondconnector. The third arm extends in a right direction and extends in thenormal direction. Similarly, a fourth arm is pivotably coupled to thesecond connector. The fourth arm extends in a left direction opposite tothe right direction and extends in the normal direction. Each of thepair of second mounting members is coupled to a respective second end ofthe third and fourth arms. Each of the pair of second wheels is coupledto a respective second mounting member. Each of the right and leftdirections is perpendicular to both of the forward direction and thenormal direction. The third and fourth arms pivot with a second degreeof freedom in the right and left directions, respectively.

In another embodiment, a system is configured to traverse a testsurface. The system includes a housing, a drive wheel rotatably coupledto the housing and configured to traverse the test surface, and anassembly disposed within the housing. The assembly comprises a firstconnector, first and second arms, a pair of first mounting members, apair of first wheels, and a holder. The first arm is pivotably coupledto the first connector at a first end thereof. The first arm extends ina forward direction and extends in a normal direction perpendicular tothe forward direction and normal to the test surface. Similarly, thesecond arm is pivotably coupled to the first connector at a first endthereof. The second arm extends in a rearward direction opposite to theforward direction and extending in the normal direction. The pivotablecoupling of the first and second arms to the first connector passivelynormalizes a detection direction of the probe towards the test surfaceas the system with the probe traverses the test surface in response torotation of the drive wheel.

In more particular embodiments, a system as described above can includea linear motion guide configured to guide the assembly linearly relativeto the housing. The system can further include a compression-basedresilient member disposed between a top surface of the assembly and aninterior surface of the housing. The pair of first wheels can becasters. The holder can be coupled to a rotating shaft of the probe andconfigured to allow the probe to rotate around the rotating shaft. Afirst resilient member can be connected to each of the first and secondarms. The first resilient member can be configured to bias the first andsecond arms towards each other. A given embodiment can include any oneor more of the foregoing further features, connections and arrangements.

In a further embodiment, a method is configured to inspect a testsurface. The method comprises providing a housing having a drive wheelrotatably coupled to the housing and configured to traverse the testsurface, and providing an assembly disposed within the housing. Theassembly includes a first connector, a first arm, a second arm, a pairof first mounting members, a pair of first wheels, and a holder. Thefirst arm is pivotably coupled to the first connector at a first endthereof. The first arm extends in a forward direction and extends in anormal direction perpendicular to the forward direction and normal tothe test surface. Similarly, a second arm is pivotably coupled to thesecond connector at a first end thereof. The second arm extends in arearward direction opposite to the forward direction and extends in thenormal direction. Each of the pair of first mounting members is coupledto a respective second end of the first and second arms. Each of thepair of first wheels is coupled to a respective first mounting member.The holder is coupled to the first connector and is configured to hold aprobe adjacent to the test surface.

The method according to this disclosure further comprises traversing thetest surface by operation of the drive wheel, pivoting the first andsecond arms, and passively normalizing a detection direction of theprobe within the holder towards the test surface as the probe inspectsthe test surface. In more particular embodiments, the method can furtherinclude biasing the first and second arms towards each other by a firstresilient member.

Any combinations of the various embodiments and implementationsdisclosed herein can be used in a further embodiment, consistent withthe disclosure. These and other aspects and features can be appreciatedfrom the following description of certain embodiments presented hereinin accordance with the disclosure and the accompanying drawings andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side schematic view of a crawler system having a passivenormalization assembly traversing a curved surface, according to anembodiment.

FIG. 2 is a side schematic view of the crawler system of FIG. 1traversing a flat surface, according to the embodiment.

FIG. 3 is a top rear side perspective view of the passive normalizationassembly, according to the embodiment.

FIG. 4 is a side plan view of the passive normalization assembly of FIG.3, according to the embodiment.

FIG. 5 is a top rear side perspective view of a portion of the passivenormalization assembly with parts separated, according to theembodiment.

FIG. 6 is a top rear side perspective view of the portion of the passivenormalization assembly of FIG. 5 with parts assembled, according to theembodiment.

FIG. 7 is a side plan view of the passive normalization assembly of FIG.3 in a frame in a first configuration, according to the embodiment.

FIG. 8 is a side plan view of the passive normalization assembly of FIG.3 in a frame in a second configuration, according to the embodiment.

FIG. 9 is a side plan view of the passive normalization assembly of FIG.3 in a frame in a third configuration, according to the embodiment.

FIG. 10 is a rear plan view of a passive normalization assembly in aframe, according to an alternative embodiment.

FIG. 11 is a top rear side perspective view of the passive normalizationassembly in the frame shown in FIG. 10, according to the alternativeembodiment.

FIG. 12 is a flowchart of operation of the system having the passivenormalization assembly of FIGS. 1-11.

FIGS. 13-19 are side schematic views of alternative embodiments of thecrawler of FIGS. 1-2 illustrating symmetry-preserving mechanisms.

It is noted that the drawings are illustrative and are not necessarilyto scale.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE DISCLOSURE

Example embodiments consistent with the teachings included in thepresent disclosure are directed to a system and method which passivelynormalize an ultrasonic dry coupled wheel probe as the probe traverses asurface of a structure to inspect the structure, such as a flatstructure or a curved pipe. At least a pair of arms are configured topassively maintain normalization of the probe in a detection directionnormal to the surface.

As shown in FIGS. 1-9 in one embodiment, a system 10 is configured as acrawler device having a probe 12. The system 10 traverses a test surface14 of a structure 16. The probe 12 is adjacent to the test surface 14and inspects the structure 16. The probe 12 can be a wheel probe. Forexample, the probe 12 can be an ultrasonic dry coupled wheel probe.Alternatively, other types of probes can be used as the probe 12. Asshown in FIG. 1, the system 10 traverses a curved surface 14. As shownin FIG. 2, the system 10 traverses a substantially flat surface 18 of astructure 20.

As shown in FIGS. 1-2, the system 10 includes a housing 22, a drivewheel 24, and an assembly 26. The drive wheel 24 is rotatably coupled tothe housing 22. The drive wheel 24 is configured to traverse the testsurface 14, 18. The assembly 26 is disposed within the housing 22. Thesystem 10 can further include a linear motion guide 28 configured toguide the assembly 26 linearly relative to the housing 22, for example,in a vertical direction 30. The linear motion guide 28 can be affixedwithin the housing 22. The system 10 can further include acompression-based resilient member 32 disposed between a top surface 34of the assembly 26 and an interior surface 36 of the housing 22, withone surface braced against the top surface 34 or structures that arefixedly attached to the housing 22. The interior surface 36 can be anundersurface of the linear motion guide 28. The compression-basedresilient member 32 can allow the assembly 26 to move upward anddownward against the restoring force of the resilient member. Theresilient member 32 provides a pushing force downwards on the assembly26. The pushing force ensures the probe 12 maintains contact with thesurface 14, 18 as the system 10 moves along the surface 14, 18regardless of changes in the topology of the surface being traversed.The resilient member 32 can also prevent the assembly 26 from hittingagainst the interior surface 36 as the assembly 26 moves linearlyrelative to the housing 22. In an alternative embodiment, the resilientmember 32 can be a piston-cylinder device filled with compressed gas orvacuum which is arranged to provide a restoring force as describedabove.

Referring to FIGS. 3-6, the assembly 26 includes a rightward set ofcomponents 40-46, 54-58 which form a rightward portion of the assembly26, as shown in particular in FIG. 6. Similarly, a leftward set ofcomponents of the assembly 26 are mirror images of the rightward set ofcomponents 40-46, 54-58. Accordingly, the leftward set of components,once assembled, form a leftward portion of the assembly 26, which is amirror image of the rightward portion of the assembly 26 shown in FIG.6. The rightward and leftward portions are then assembled to form theoverall assembly 26, as shown in FIG. 3. The rightward and leftwardportions can be fastened together at the mounting members 46, 48,described below, using any known fastening mechanism.

Referring to the rightward portion shown in FIGS. 3-6, which is a mirrorimage of the leftward portion, the assembly 26 comprises a firstconnector 40, a first arm 42, a second arm 44, a pair of first mountingmembers 46, 48, a pair of first wheels 50, 52, and a holder 54. Thefirst arm 42 is pivotably coupled to the first connector 40 at a firstend 56 thereof. As shown in FIG. 3, the first arm 42 extends in aforward direction, and extends in a normal direction perpendicular tothe forward direction and normal to the test surface 14, 18. Similarly,the second arm 44 is pivotably coupled to the first connector 40 at afirst end 58 thereof. The second arm 44 extends in a rearward directionopposite to the forward direction and extending in the normal direction.The pivotable coupling of the first arm 42 and the second arm 44 to thefirst connector 40 passively normalizes a detection direction of theprobe 12 towards the test surface 14, 18 as the system 10 with the probe12 traverses the test surface 14, 18 in response to rotation of thedrive wheel 24.

At least one fastener 60, 62 pivotably couples the first ends 56, 58 tothe first connector 40, respectively. Each fastener 60, 62 defines arespective pivot point of the arms 42, 44 on the first connector 40. Thefasteners 60, 62 can also include pinion gears in a pinion gearassembly. The first ends 56, 58 of the arms 42, 44 are coupled togetherat the pinion gear assembly. The pinion gear assembly can be rigidlyattached to the holder 54, described below, to allow the holder 54 torotate along with the arms 42, 44, as shown in FIGS. 7-9. Such rotationof the holder 54 adjusts the angle of normalization of the probe 12.Accordingly, when both of the wheels 50, 52 are on the same horizontalsurface 18, such as shown in FIGS. 2 and 4, the holder 54 has a verticalor normal orientation to the surface 18. When the wheels 50, 52 aretilted upward or downward due to the curvature of the surface, such asthe surface 14 in FIG. 1, the holder 54 has the same tilt angle as thewheels 50, 52 since the holder 54 is rigidly coupled to the arms 42, 44by the pinion gear assembly at the first connector 40.

The pair of first wheels 50, 52 can be casters held by the mountingmembers 46, 48, respectively, at second ends 47, 49 of the arms 42, 44,respectively. Alternatively, other known types of wheels can be held bythe mounting members 46, 48, such that the wheels are free to rotate andto roll on the test surfaces 14, 18. The configuration of the arms 42,44 and the respective first wheels 50, 52 as casters balance theassembly 26. Such balancing provides a symmetry-preserving mechanism. Asthe diameter of the structure 16, 20 changes, and so the curvature ofthe surface 14, 18 changes, respectively, the preservation of symmetryallows the wheels 50, 52 to stay in contact with the surface 14, 18. Inaddition, the symmetry of the arms 42, 44 and the wheels 50, 52 alsopreserves the perpendicularity of the assembly 26 to the surface 14, 18,and so the probe 12 stays normal to the surface 14, 18.

The holder 54 can be coupled to a rotating shaft 64 of the probe 12 andconfigured to allow the probe 12 to rotate around the rotating shaft 64.As shown in FIG. 4, an optional first resilient member 66 can beconnected to each of the arms 42, 44 at fasteners 68, 70 on eachrespective arm 42, 44. The first resilient member 66 can be a spring,such as a tension spring. The first resilient member 66 can beconfigured to bias the arms 42, 44 towards each other.

As shown in FIGS. 1-2 and 7-9, the assembly 26 of FIGS. 3-6 can bemounted in a frame 72 having a top member 74 upon which the resilientmember 32 is disposed. The frame 72 can also include a guidance slot 76.The guidance slot 76 permits the first connector 40 to move within alimited curved path which defines the location of the pivot point of thearms 42, 44. A center line from a midpoint of the first connector 40 toa center of the shaft 64 substantially defines the normal direction.

In operation, as the wheels 50, 52 traverse the surface 14, 18, the arms42, 44 pivot about their respective pivot points on the first connector40, defined by the fasteners 60, 62. The arms 42, 44 flex in asymmetrical manner toward or away from the center line, which passivelynormalizes the detection direction of the probe 12 to be substantiallyparallel to the normal direction.

In an alternative embodiment shown in FIGS. 10-11, the system 10 furtherincludes an assembly 80 having a second connector 82, a third arm 84, afourth arm 86, a pair of second mounting members 88, 90, and a pair ofsecond wheels 92, 94. The third arm 84 is pivotably coupled to thesecond connector 82 at a first end 91. The third arm 84 extends in aright direction and extends in the normal direction. Similarly, thefourth arm 86 is pivotably coupled to the second connector 82 at asecond end 93. The fourth arm 86 extends in a left direction opposite tothe right direction and extends in the normal direction. Each of thepair of second mounting members 88, 90 is coupled to a respective secondend 96, 98 of the arms 84, 86. Each of the pair of second wheels 92, 94is coupled to a respective second mounting member 88, 90. Each of theright and left directions is perpendicular to both of the forwarddirection and the normal direction, as shown in FIG. 11. The arms 84, 86pivot with a second degree of freedom in the right and left directions,respectively.

In another embodiment, a method 100 includes providing, in step 110, ahousing 22 having a drive wheel 24 rotatably coupled to the housing 22.The method 100 also includes providing, in step 120, an assembly 26disposed within the housing 22 with pivoting arms 42, 44 and a holder 54holding a probe 12 adjacent to a test surface 14, 18. The method 100then has at least the probe 12 traverse the test surface 14, 18 in step130. The method 100 then pivots the arms 42, 44 in step 140 in responseto changes in curvature of the test surfaces 14, 18. The method 100 thenpassively normalizes the detection direction of the probe 12, in step150, towards the test surface 14, 18 as the probe 12 inspects the testsurface 14, 18.

Portions of the methods described herein can be performed by software orfirmware in machine readable form on a tangible (e.g., non-transitory)storage medium. For example, the software or firmware can be in the formof a computer program including computer program code adapted to causethe system and assembly to perform various actions described herein whenthe program is run on a computer or suitable hardware device, and wherethe computer program can be embodied on a computer readable medium.Examples of tangible storage media include computer storage deviceshaving computer-readable media such as disks, thumb drives, flashmemory, and the like, and do not include propagated signals. Propagatedsignals can be present in a tangible storage media. The software can besuitable for execution on a parallel processor or a serial processorsuch that various actions described herein can be carried out in anysuitable order, or simultaneously.

FIGS. 13-19 illustrate alternative embodiments of the system 10 of FIGS.1-2, utilizing symmetry-preserving mechanisms in the housing 22. Each ofthe symmetry-preserving mechanisms in FIGS. 13-19 utilize one or more ofa resilient member, a linkage, a magnet, and, optionally, gravity (whenthe system is situated on top of a structure) to balance the wheels 50,52 on either side of the probe 12 whether the system 10 is on a curvedsurface 14 or a flat surface 18. The configuration of the wheels 50, 52on the surface 14, 18 changes such that movement of the wheel 50 in afirst direction relative to the probe 12 is mirrored by movement of thewheel 52 in a second direction relative to the probe 12, with the seconddirection mirroring the first direction about an axis of the probe 12.The axis of the probe passes through the shaft 64. The axis isillustrated by the dotted lines in FIGS. 7-9. Such mirrored movement ofthe wheels 50, 52, caused by each symmetry-preserving mechanism,maintains the probe 12 in continuous contact with the respective surface14, 18. As shown in FIGS. 13-17, the continuous contact can bemaintained by a push-down compression mechanism, such as a resilientmember in the form of a spring. As shown in FIGS. 18-19, the continuouscontact can be maintained by a magnet.

The symmetry-preserving mechanisms described herein maintain thesymmetry of the wheels 50, 52 and their arms 42, 44 independent ofgravity. However, depending on the orientation of the surfaces 14, 18,gravity can provide additional symmetry-preserving forces on the wheels50, 52 and arms 42, 44. In addition, the symmetry-preserving mechanismsdescribed herein dynamically adjust the configuration of the wheels 50,52 as the wheels 50, 52 move along the surfaces 14, 18 having differentcurvatures. Such dynamic adjustment passively normalizes the probe 12without actuators. Accordingly, the symmetry-preserving mechanismsdescribed herein are less costly to implement than known normalizationsystems.

Referring in greater detail to the embodiments in FIGS. 13-19, thesystem in FIG. 13 has a mechanism 200 configured to have the wheels 50,52 move in symmetrical linear paths 205, 206 due to and symmetricallinkages. The system in FIG. 14 has a mechanism 210 configured to havethe wheels 50, 52 move in symmetrical diagonal paths 215, 216 due tosymmetrical linkages. The system in FIG. 15 has a mechanism 220configured to have the wheels 50, 52 move in symmetrical arc paths 225,226 due to symmetrical linkages with pivot points. The system in FIG. 16has a mechanism 230 similar to the mechanism 200 in FIG. 13. Themechanism 230 has the wheels 50, 52 move in symmetrical linear paths231, 232 due to symmetrical resilient linkages using a dedicated linearguide 233, 234 for each wheel 50, 52, respectively. The wheels 50, 52are connected to each other by a translational link 235 between thewheels 50, 52. Resilient members 236, 237 are provided between thetranslational link 235 and the housing 22. The resilient members 236,237 can be compression springs. The system in FIG. 17 has a mechanism240 similar to the system 10 in FIGS. 1-2 using swing arms 42, 44, withthe wheels 50, 52 moving in symmetrical arc paths due to symmetricallinks 241, 242. However, compared to the mechanism in FIGS. 1-2, themechanism 240 in FIG. 17 includes a coupling between the arms 42, 44using links 241, 242, respectively, and grounded revolute joints 243,244, respectively, with a tension spring 245 between the arms 42, 44.

The systems in FIGS. 18-19 use magnets to maintain strong contactbetween the probe 12 and the surfaces 14, 18. The wheels 50, 52 move insymmetrical arc paths due to magnetic forces on the linkages attached tothe wheels 50, 52. The system in FIG. 18 has a mechanism 250 with twofixed magnetic disks on the shaft 64 of the probe 12, on either lateralside of the probe 12. FIG. 18 illustrates the magnetic disk 255 on arightward side of the probe 12. One of the two poles S, N on eachmagnetic disk 255 provides a magnetic force to align the pole with thesurface 14, 18. For example, as shown in FIG. 18, the north pole N ofthe magnetic disk 255 is aligned with the surface 14, 18. Alternatively,the system in FIG. 19 has a mechanism 260 with a static ring magnet 265mounted rigidly to the shaft 64. The wheel 266 of the probe 12 sitsinside a hole 267 in the ring magnet 265, with the ring magnet 265surrounding a lower part of the wheel 266 of the probe 12. The ringmagnet 265 creates a magnetic pulling force for the probe 12 to maintainthe probe 12 in continuous contact with the surface 14, 18. In anexample embodiment, the ring magnet 265 is diametrically magnetized,with the north pole disposed laterally to the right and the south poledisposed laterally to the left in FIG. 19. In another exampleembodiment, the ring magnet 265 can be axially magnetized, with thenorth pole disposed upward along the normal direction, and the southpole disposed downward along the normal direction.

It is to be further understood that like or similar numerals in thedrawings represent like or similar elements through the several figures,and that not all components or steps described and illustrated withreference to the figures are required for all embodiments orarrangements.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “contains”,“containing”, “includes”, “including,” “comprises”, and/or “comprising,”and variations thereof, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Terms of orientation are used herein merely for purposes of conventionand referencing and are not to be construed as limiting. However, it isrecognized these terms could be used with reference to an operator oruser. Accordingly, no limitations are implied or to be inferred. Inaddition, the use of ordinal numbers (e.g., first, second, third) is fordistinction and not counting. For example, the use of “third” does notimply there is a corresponding “first” or “second.” Also, thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

While the disclosure has described several exemplary embodiments, itwill be understood by those skilled in the art that various changes canbe made, and equivalents can be substituted for elements thereof,without departing from the spirit and scope of the invention. Inaddition, many modifications will be appreciated by those skilled in theart to adapt a particular instrument, situation, or material toembodiments of the disclosure without departing from the essential scopethereof. Therefore, it is intended that the invention not be limited tothe particular embodiments disclosed, or to the best mode contemplatedfor carrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

The subject matter described above is provided by way of illustrationonly and should not be construed as limiting. Various modifications andchanges can be made to the subject matter described herein withoutfollowing the example embodiments and applications illustrated anddescribed, and without departing from the true spirit and scope of theinvention encompassed by the present disclosure, which is defined by theset of recitations in the following claims and by structures andfunctions or steps which are equivalent to these recitations.

What is claimed is:
 1. An assembly configured to hold a probe adjacentto a test surface, comprising: a first connector; a first arm pivotablycoupled to the first connector at a first end thereof, the first armextending in a forward direction and extending in a normal directionperpendicular to the forward direction and normal to the test surface; asecond arm pivotably coupled to the first connector at a first endthereof, the second arm extending in a rearward direction opposite tothe forward direction and extending in the normal direction; a pair offirst mounting members each coupled to a respective second end of thefirst and second arms; a pair of first wheels each coupled to arespective first mounting member; and a holder coupled to the firstconnector and configured to hold the probe, wherein the pivotablecoupling of the first and second arms to the first connector passivelynormalizes a detection direction of the probe as the probe traverses thetest surface.
 2. The assembly of claim 1, further comprising: a firstresilient member connected to each of the first and second arms andconfigured to bias the first and second arms towards each other.
 3. Theassembly of claim 1, wherein the pair of first wheels are casters. 4.The assembly of claim 1, wherein the holder is coupled to a rotatingshaft of the probe and configured to allow the probe to rotate aroundthe rotating shaft.
 5. The assembly of claim 1, wherein the firstconnector includes a first pinion gear.
 6. The assembly of claim 1,wherein the first and second arms pivot with a first degree of freedomin the forward and rearward directions, respectively.
 7. The assembly ofclaim 1, further comprising: a second connector; a third arm pivotablycoupled to the second connector, the third arm extending in a rightdirection and extending in the normal direction; a fourth arm pivotablycoupled to the second connector, the fourth arm extending in a leftdirection opposite to the right direction and extending in the normaldirection; a pair of second mounting members each coupled to arespective second end of the third and fourth arms; and a pair of secondwheels each coupled to a respective second mounting member.
 8. Theassembly of claim 7, wherein each of the right and left directions isperpendicular to both of the forward direction and the normal direction.9. The assembly of claim 8, wherein the third and fourth arms pivot witha second degree of freedom in the right and left directions,respectively.
 10. A system configured to traverse a test surface,comprising: a housing: a drive wheel rotatably coupled to the housingand configured to traverse the test surface; and an assembly disposedwithin the housing and comprising: a first connector; a first armpivotably connected to the first connector at a first end thereof, thefirst arm extending in a forward direction and extending in a normaldirection perpendicular to the forward direction and normal to the testsurface; a second arm pivotably connected to the second connector at afirst end thereof, the second arm extending in a rearward directionopposite to the forward direction and extending in the normal direction;a pair of first mounting members each coupled to a respective second endof the first and second arms; a pair of first wheels each coupled to arespective first mounting member; and a holder coupled to the firstconnector and configured to hold a probe adjacent to the test surface,wherein the pivotable coupling of the first and second arms to the firstconnector passively normalizes a detection direction of the probetowards the test surface as the system with the probe traverses the testsurface in response to rotation of the drive wheel.
 11. The system ofclaim 10, further comprising: a linear motion guide affixed within thehousing and configured to guide the assembly linearly relative to thehousing.
 12. The system of claim 10, further comprising: acompression-based resilient member disposed between a top surface of theassembly and an interior surface of the housing.
 13. The system of claim10, wherein the pair of first wheels are casters.
 14. The system ofclaim 10, wherein the holder is coupled to a rotating shaft of the probeand configured to allow the probe to rotate around the rotating shaft.15. The system of claim 10, further comprising: a first resilient memberconnected to each of the first and second arms and configured to biasthe first and second arms towards each other.
 16. The system of claim10, further comprising: a second connector; a third arm pivotablycoupled to the second connector, the third arm extending in a rightdirection and extending in the normal direction; a fourth arm pivotablycoupled to the second connector, the fourth arm extending in a leftdirection opposite to the right direction and extending in the normaldirection; a pair of second mounting members each coupled to arespective second end of the third and fourth arms; and a pair of secondwheels each coupled to a respective second mounting member.
 17. Thesystem of claim 16, wherein each of the right and left directions isperpendicular to both of the forward direction and the normal direction.18. The system of claim 17, wherein the third and fourth arms pivot witha second degree of freedom in the right and left directions,respectively.
 19. An assembly configured to hold a probe adjacent to atest surface, comprising: a symmetry-preserving sub-assembly; a firstarm coupled to the symmetry-preserving sub-assembly, the first armextending in a forward direction and extending in a normal directionperpendicular to the forward direction and normal to the test surface; asecond arm coupled to the symmetry-preserving sub-assembly, the secondarm extending in a rearward direction opposite to the forward directionand extending in the normal direction; a first wheel coupled to an endof the first arm and configured to move on the test surface; a secondwheel coupled to an end of the second arm and configured to move on thetest surface; and a holder coupled to the symmetry-preservingsub-assembly and configured to hold the probe, wherein the coupling ofthe first and second arms to the symmetry-preserving sub-assemblymaintains a symmetrical configuration of the first and second arms aboutan axis through the holder to passively normalize a detection directionof the probe as the probe traverses the test surface.
 20. The assemblyof claim 19, wherein as a curvature of the test surface changes,movement of the first arm in a first direction relative to the probe, asthe first wheel traverses the test surface, is mirrored by thesymmetry-preserving sub-assembly to move the second arm in a seconddirection relative to the probe with the second direction mirroring thefirst direction about the axis as the second wheel traverses the testsurface.